This invention pertains to a PWM cycloconverter or matrix converter using multiple converters arranged in parallel and coupled by a reactive element.
FIG. 6 illustrates an example of a conventional PWM cycloconverter or matrix converter. In FIG. 6, (1) represents a 3-phase AC power source; (2) represents an LC filter; (3) represents a converter composed of nine bi-directional switches (10); and (4) represents a load. For example, the bi-directional switches (10) that form converter (3) may have the constitution shown in FIG. 7. In FIG. 7, (5) and (6) represent unidirectional IGBTs (insulating gate bipolar transistor), and (7) and (8) represent diodes. Each bi-directional switch (10) can turn ON/OFF current either direction under gate signals.
The voltage type PWM converter/PWM inverter system shown in FIG. 8 was developed a long time ago, and many products, ranging from those with small capacity to those with large capacity have been manufactured.
However, in order to rectify an AC input to DC with a converter and then to convert the DC to AC with an inverter, DC capacitors (9) are needed. However, DC capacitors not only occupy a certain space, for electrolytic capacitors, their lifetime is a problem.
On the other hand, for a PWM cycloconverter, there is no need to use DC capacitors, and there is no problem with respect to lifetime. However, it is still under study and there are only reports on small-capacity equipment at the laboratory level (for example, S. Ishii, E. Yamamoto, H. Hara, E. Wantanata, A. M. Hava, and X. Xia, xe2x80x9cA Vector Controlled High Performance Matrix Converterxe2x80x94Induction Motor Drivexe2x80x9d, Conference record of IPEC-Tokyo, pp. 235-240. April, 2000).
For a PWM cycloconverter, it is necessary to avoid an open circuit of the output terminals and a short circuit on the input side. A high-current stack containing a snubber is formed but this is difficult to realize in principle. As a result, it is difficult to manufacture a converter with a high capacity. This is undesired. The objective of this invention is to solve the aforementioned problems.
In order to solve the aforementioned problems, the invention described herein provides a type of multiple PWM cycloconverter with the following constitution: for p unit converters of an n-input/m-output PWM cycloconverter composed of n*m bi-directional switches (n, m and p are integers of 2 or larger, respectively), the various phase output terminals are connected in parallel via reactors, and there are m output terminals in all.
The reactors for parallel connection may share a core for each output terminal and a current sensor is set for each output phase of each unit converter to detect current, and the output voltage command for each unit converter is corrected corresponding to a current unbalance.
According to this invention, plural PWM cycloconverters (matrix converters) are set in parallel via reactors. Consequently, a large-capacity converter is realized. Because for a PWM cycloconverter, an AC input is directly converted to an AC output, there is no need to use capacitors in the DC link portion. As a result, the size and cost of the converter can be reduced. Also, it is free of problems pertaining to lifetime. Also, there is no need to have a capacitor preparatory charging circuit before the start of operation.